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Abstract:
Seismological and other geophysical observations from the surface show that the internal structure of our planet consists of concentric layers: the crust (on which we live), the mantle and a metallic core. However, even the deepest drill holes can access less than 1 percent of the Earth depth for chemical/physical measurements or sampling. A multidisciplinary approach combining geophysics,
geochemistry, petrology and geodynamic modeling is required in order learn more about the deep Earth.
Mineral physics provides data at high pressure measured in the laboratory. High pressure measurements performed at the GFZ in the framework of an international cooperation showed that the spin transition of divalent iron in ferropericlase (Mg,Fe)O has a major effect on the elastic properties at conditions existing in the lower mantle. This spin transition of (Mg,Fe)O is caused by a pressure induced spin pairing of the 3d electrons between 40 and 60 GPa. The measurements showed that the bulk modulus and the density of ferropericlase increase by several percent at this pressure regime. Moreover, the shear wave velocity anisotropy increases by about 60 % in the same pressure range. These results suggest that the anisotropy in lowermost mantle is caused by the texture of the ferropericlase rather than by perovskite that is about four times more abundant.
Additional new experiments performed on a synthetic mantle rock at the synchrotron light source PETRA III (DESY, Hamburg) have the potential to reveal the development of texture in rocks subject to the extreme pressures and temperatures conditions present in the very deep mantle of the Earth.
